The 4 Month Sleep Regression: Why it Happens & How You Can Help!


Written By: Jamie Labbe, MS
Owner/Founder of Oh Baby Consulting
Pediatric Sleep Consultant

As a pediatric sleep specialist, one of most common things I get asked about is whether there is an “X month sleep regression.” The short answer is yes as there are certainly noticeable sleep disruptions when your baby is working on a new skill or going through a mental leap. However, it’s actually a bit more complex than that. Though most true sleep regressions are due to progressions in other areas of your child’s development and normally subside within 1-2 weeks (if your little one was a good sleeper to begin with), there is one “regression” that is different from the rest in that it is a total reorganization of your baby’s brain and sleep cycles. That is the 4-month sleep regression.

WHY IT HAPPENS: The science behind the 4-month sleep regression

Most of us think of sleep in black and white terms: we’re either asleep or we’re awake. But in reality, that cannot be farther from the truth. We actually all sleep in stages ranging from light sleep to deep sleep, and several of these stages make up one sleep cycle. A full night of sleep is actually stringing together several of these sleep cycles. When babies are born and for the first several weeks of their lives, their sleep is drastically different from the sleep of older babies, toddlers, children, teenagers, and adults. Newborns really only have two stages of sleep and spend about 50% of their time in deeper sleep. Because they sleep so deeply, it’s much easier for them to sleep anywhere (like out to brunch or on the beach.) However, when babies undergo the biological shifts that occur around 4 months, they “graduate” to a four-stage sleep cycle – with only 25% of it being deep – that they will follow for the rest of their lives.

A baby’s sleep cycle is between 30-60 minutes and in between each cycle, they will have a “partial wake up” as they transition into the next one. Adult sleep cycles are longer, but we do this too! However, these wakes are usually so benign that we just roll over and continue sleeping, never remembering them in the morning. If, in between sleep cycles, things were different than they were when we fell asleep – the lights were on, our pillow was on the floor, or we were suddenly on our couch when we had fallen asleep in our bed – that can be startling enough to wake us up fully.

The same is true for babies. If they wake up in their crib and the last thing they remember is being in your arms, they’re more likely to wake up fully vs. transitioning seamlessly between sleep cycles. As adults, we have skills that we can recall to get ourselves back to sleep when these wake-ups happen, but babies who have yet to learn these skills get stuck and will then need help getting back to sleep just like they did at the beginning of the night.

HOW TO HELP: Navigating through the 4-month sleep changes
1. Make the room DARK. 

While your sleepy newborn was likely able to easily snooze anywhere, the older your baby is the more sensitive they can become to their environment. Light tells our brains that it’s time for activity and alertness and the brain secretes hormones accordingly. Similarly, darkness allows sleep-inducing hormones to rise. To make sleep as easy as possible for your baby, it’s best to keep their room absolutely dark during nights and naps. It can be helpful to use the hand test when determining if your baby’s room is dark enough. After turning off all the lights and closing the shades, can you see your hand in front of your face? If the answer is yes, I would recommend investing in blackout shades. In a pinch, black garbage bags or even tinfoil will do the trick. During sleep times, your baby should not be able to tell whether it’s midnight or noon in their room.

2. Maintain an appropriate schedule: 

One of the easiest ways help your baby sleep better is by making sure they’re not getting overtired in between naps or before bedtime. When babies are overtired, their bodies will secrete hormones to keep them awake and alert. This can be extremely counterproductive to both falling asleep and staying asleep as your baby will be tired, but their body will be working against them. At 4 months old, most babies can tolerate an average of 2 hours of awake time between naps and before bed.

3. Follow a consistent bedtime routine

Routines cue the brain & body that we are transitioning out of day and into night sleep. (This is true for adults too!) Pick 4-5 steps lasting 20-30 minutes (including a final feed) that you can do sequentially night after night to help your baby prepare for bedtime.

4. Practice independent sleep skills

Up until this point, you may have had to help your baby transition from awake to asleep as they did not have the skills to do it on their own yet. During the newborn stage, you may have gotten into the habit of feeding, rocking, or bouncing your baby to drowsiness or to sleep before laying them down. Around 4 months, there is a cognitive surge and babies become much more aware of their surroundings and can begin to rely heavily on those external strategies you are using to help them get to sleep at bedtime. If those external strategies that were present when they first fall asleep are no longer present in between sleep cycles an hour later, babies are more likely to wake up. Without having the skills to get themselves into their next sleep cycle, they are likely to struggle and will need your help getting back to sleep. 

Putting your baby down awake helps encourage them to fall asleep independently so they can skill build and then recall those skills as they transition between sleep cycles throughout the night. This way, they only wake up for any developmentally appropriate feeds, a true need, or when they’re ready to be up for the day and not just because they aren’t sure how to continue their sleep.

Some babies do very well adjusting to the changes that the 4-month sleep regression ushers in while other babies will have a harder time. Practicing these 4 tips is a great place to start and know that there are always more resources and help out there if you feel stuck. You’re never alone!

Jamie Labbe, MS is a pediatric sleep consultant and owner of Oh Baby Consulting. She helps parents whose babies and toddlers are struggling with sleep find solutions that work for their family so that everyone can get the rest they need. Her goal is to take the stress & overwhelm out of the whole “sleep thing” and give families the confidence and clarity to navigate this piece of parenthood.